A new modulestore backed by mongo that changes the data format to
facilitate easy versioning, sharing content between courses, and fast
lookup of course structure and Scope.settings data.

Conflicts:
	cms/djangoapps/contentstore/tests/test_contentstore.py

https://edx-wiki.atlassian.net/browse/STUD-428

Embed a chat widget (much like the calculator widget) into the
courseware. To use, you must point it at an ejabberd box,
configured as `JABBER_DOMAIN` in the settings.

Update existing tests and provide new ones to test new paradigm.

Refactor new set_many and update XBlock version number.

fix test to use the new create_item method rather than clone_item, which has been deprecated, and thus breaking the test

add a default XML serialization if the 'data' field is empty or None. Some XModules now - like video XModule - do not have XML set in the 'data' field

Add boilerplate option to ItemFactory
Minor start date fix to not use microsecs

The defaults used to be rerandomize=always, showanswer=closed. This is
preserved for capa problems being imported from XML. However, for
courses, and for problems created in Studio, the default has been
changed to never/finished, to match the previous defaults used by
Studio.

Instead, we use XModule field default values when creating an empty
XModule. Driven by this use case, we also allow for XModules to be
created in memory without being persisted to the database at all. This
necessitates a change to the Modulestore api, replacing clone_item with
create_draft and save_xmodule.

This standardizes the XModule field default values to be the same as the
values that are presented by studio when a component is added to a
course.

DraftModuleStore was originally designed as a mixin, but never used that
way, and with the upcoming changes to use the versioned module store,
never will be. This changes removes a circular dependency between
mongo.py and draft.py.